Magnetostrictive signal translating apparatus



Patented Jan- 21, 194"? FlCE mecnnrosmrorrvn SIIGNAL mansrn'rmo APPARATUS Harry F. Olson, Princeton, N. 3., and Frank A. Hester, New York, N. Y., assignors to Radio Corporation of America, a corporation of Dela- Application December 30, 1944. Seriai No. 5703M with which acoustically responsive devices; such as microphones, are useful. For example, a microphone the output of which is connected to a mine or other explosive charge may be used to detect the presence of a sound emitting target which it is desired to destroy. For this purpose,

it is enerally necessary, to provide a microphone which is mailed in construction and which has good sensitivity.

The primary object of our present invention is to provide an im roved, magnetostriction microphone which will have these characteristics, among others.

More particularly. it is an object of our present invention to provide an improved, magnetostriction microphone which can be used to detect submarine objects with great efficiency. and which will withstand considerable abuse without becoming defective. 1

Another object of our present invention is to prov de an improved magnetrostriction microphone as aforesaid which is particularly useful in connection with mines or other explosive charges.

Still another object of our present invention is to provide an improved magnetostriction microphone ,as set forth above wh ch is very simple in construction and economical in cost.

In accordance with our present invention, the microphone consists of a hollow cylinder of nickel or other ma netostrictive material adapted to vibrate radially under the influence of sound waves impinging thereon. Within the cylinder. we provide a magnetic structure which consists of a laminated core extending diametrically across the cylinder and including a polarizing magnet, the core engaging the interior surface of the cylinder at diametrically opposite points lengthwise thereof. The complete magnetic circuit comprises the polarizing magnet, which may be of laminated Alnico, if desired, the core, which may be of silicon steel laminations, and thecylindrical magnetostrictive tube. plies a polarizing flux through the cylinder. Around the core structure is a signal coil or winding which may be suitably connected to an external amplifier. The hollow cylinder is closed ofi at each end by suitable plates or the like which have fluid-tight relation therewith, the magnetic structure and the coil being housed entirely with- The magnet sup 5 (Cl. 1'l7386) in ,the cylinder. If desired, the microphone may be placed in a suitable baflle.

When sound waves impinge on the cylinder, the peripher thereof is alternately contracted and expanded corresponding to the condensations and rarefactions in the sound waves. This produces a corresponding alternating change of magnetic flux in the magnetic circuit and results in the induction of an ele'ctromotive force in the coil or winding.

The novel features that we consider characteristic of our invention are set forth with particularity in the appended claims. The invention itself. however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description of one embodiment thereof, when read in connection with the accompanying drawing in which Figure 1 is a central, longitudinal sectional view, taken on the line I-I of Figure 2, of one form of microphone constructed in. accordance with our present invention,

Figure 2 is a transverse, sectional view thereof taken on the line II-II of Figure 1. and

Figure 3 is a circuit diagram illustrating how our improved microphone may be connected to an amplifying circuit.

Referring more particularly to the drawing, wherein similar reference characters designate corresponding parts throughout, there is shown a normally open-ended cylinder i of nickel or other, suitable magnetostrictive material to the ends of which are secured, by brazing or the like, a pair of rings 3. A pair of end plates 5 are secured to the rings 3 in fluid-tight relation thereto, thus closing off the interior of the cylinder I from the ambient or surrounding medium.

Within the cylinder I and extending diametrically, thereacross is a magnetic field structure comprising a plurality of oppositely disposed, substantially T-shaped laminations I and one or more permanent magnets 9. The laminations i may be formed of silicon steel, and the magnets 9, which supply a polarizing flux through the laminations i and the cylinder i, may be of Alnico, and preferably also of laminated construction. The laminations i may be stepped, as clearly shown in Figure 2, and are tightly clamped together, the longest ones being disposed in the center and substantially in the plane of the axis of the cylinder. The laminations i are arranged in two oppositely disposed groups, one or more of the longest ones of each group in a radial direction through the cylinder being so arranged that which is open at the top, the magnetostrictive cylinder I having an external diameter which is smaller than the internal diameter of the baffle.

I5 and being arranged concentrically therewith to provide an annular space. I! therebetween.

The output leads from the coil It may be brought out in the form of a cable l9 through a fluid-tight coupling 2| of any suitable construction.-

When sound waves strike the vibratory cylinder I, it vibrates radially by alternately contra'cting and expanding somewhat in correspondence with the condensations and rarefactions in the sound wave. The alternating change of magnetic flux which results in the magnetic circuit induces an electromotive force in the coil lithe output of which may be applied to an amplifier 23 or any suitable type. A microphone constructed as above has an impedance which is highly reactive. Its impedance can be reduced to the resistive component by inserting a capacitance 25 in series with the coil iii. The microphone of our present "invention is a relatively low impedance device, having a resistance of approximately ohms" at 350 cycles per second. A coupling transformer 21 may therefore be used to couple the microphone to the amplifier 23 to step up to 250,000 ohms. This confines all high impedances to the vacuum tube amplifier.

The transformer may be tuned where band pass response, is desire'd,

A microphone such as described above will be. found to be extremely rugged, as evidenced by the fact that it can be struck a relatively hard blow with a hammer and dented without appre-. ciably impairing its response. In view of the low impedance of the microphone, moisture will, not impair its performance. It will be found that a microphone of this type can be made very sensitive, and its low frequency response can be increased considerably by the addition of the baflle l5.

Although we have shown and described but a single embodiment of our present invention, it will undoubtedly be apparent to those skilled in the art that many other modifications, as well as variations in the one described herein, are possible within the scope of our invention. It will also be apparent, no doubt, that our present invention can be employed as a sound transmitter or projector, instead of as a microphone or receiver, by passing signal currents through the coil l3 which, in turn, will vary the flux in the magnetic circuit and thereby cause the cylinder l to vibrate and radiate sonic waves. Since the present ind nation of a hollow cylinder of magnetostrictive material adapted to vibrate:radially, magnetic means within sa id cylinder extending diametrically thereacross and providing a magnetic path between diametrically opposite points on said other in the region of the axis of said cylinder,

and characterized further in that said polarizing magnet comprises a permanent magnet disposed in the space between said laminations in engagement with the adjacent ends of said opposed laminations. h

3. Signal translating apparatusaccording vto claim 1 characterized in that said lamlnations, comprise substantially T-siiaped member (1) the cross arms of which are arranged lengthwise of said cylinder and are in engagement with said cylinder at said diametrically opposite points and (2) the legs of which extend radially across said cylinder toward each other in opposed relation from their respective cross arms, said legs said cylinder in fluid-tight relation thereto and closing off the interior of said cylinder from the ambient, magnetic means within said cylinder extending diametrically thereacross and providing a magnetic path between diametrically opposite points on said cylinder, said magnetic means including a polarizing magnet. a winding also within said cylinder disposed around said magnetic means, and a'bai'ile surrounding said cylinder,

said baiile having a longer cross sectional dimension than the external diameter of said cylinder whereby to provide a space between said cylin-' der and said baille.

5. In signal translating apparatus, the combination of a normally open-ended. hollow cylinder of magnetostrictive material adapted to vibrate radially, closure means secured to each end of said cylinder in fluid-tight relation thereto and closing oi! the interior of said cylinder from the ambient.'magnetic means within said cylinder extending diametrically thereacrossand providing a magnetic path between diametrically opposite points on said cylinder, said means including a polarizing magnet, a winding also within said cylinder disposed around said magnetic means, and a cylindrical bame around said cylinder in concentric relation thereto. said baiiie having a longer internal diameter than the ex- I ternal diameter of said cylinder whereby to provide an annular space therebetween.

HARRY F. OLSON. FRANK A. HESTER. 

